1. Field of the Invention
This invention relates to electrical switching apparatus such as power circuit breakers, network protectors and switches used in electric power circuits carrying large currents. More particularly, it relates to such apparatus which utilizes a large spring to store sufficient energy to close the contacts of the apparatus against both the sizeable magnetic repulsion forces generated by the large currents, and the force required to charge the open springs which subsequently open the contacts. Specifically, it relates to indicators which discretely snap between positions to display the charge state of the close spring and the open/closed state of the contacts.
2. Background Information
Electrical switching apparatus for opening and closing electric power circuits typically utilize an energy storage device in the form of one or more large springs to close the contacts of the device into the large currents which can be drawn in such circuits. Such electrical switching apparatus includes power circuit breakers or network protectors which provide protection and electrical switches which are used to energize and deenergize parts of the circuit or to transfer between alternative power sources. These power circuit breakers, network protectors and switches also include an open spring or springs which rapidly separate the contacts to interrupt current flowing in the power circuit. As indicated, either or both of the close spring and open spring can be a single spring or multiple springs and should be considered as either even though the singular is hereafter used for convenience.
The close spring in these power circuit breakers, network protectors and switches is incorporated into an operating mechanism which includes a cam mounted on a cam shaft and coupled to the close spring. The close spring is charged either by a manual charging handle or an electric motor which rotates the cam shaft. The amount of stored energy required dictates that many short strokes of the handle delivered through a rachet mechanism are needed to charge the spring manually. It also requires a low speed, high torque motor for automatic charging. The result is that a measurable length of time is required to charge the close spring, either manually or automatically.
For both operational and safety reasons, an indicator is provided to appraise the user of the charge state of the close spring. Typically, the indicator is pivotally mounted in a window in the front panel of the apparatus and rotates between display of CHARGED and DISCHARGED legends reflecting the charge state of the close spring. It is common for the indicator to be driven off of the charge cam shaft. As discussed, the cam shaft rotates relatively slowly during charging. Thus, the indicator rotates slowly and for a time simultaneously presents parts of both the CHARGED and DISCHARGED legends.
Typically, such electrical switching apparatus also has an indicator providing a visual indication of the open/closed state of the contacts. If the contacts should become welded closed, such as due to arcing, it is possible for the operating mechanism to be operated to the open position even through the contacts remain closed.
There is a need, therefore, for improved indicators for displaying the condition of electrical switching apparatus.
Specifically, there is a need for an improved indicator for displaying the charge state of the close spring of power circuit breakers, network protectors and switches.
In particular, there is a need for an improved indicator which unambiguously and accurately displays the close spring charge state.
There is a more specific need for such an indicator with discrete positions for displaying either the CHARGED or DISCHARGED state of the close spring.
In this regard, there is a need for an indicator which discretely snaps from display of one legend to the other and particularly in transitioning from display of the DISCHARGED indication to the CHARGED indication.
There is also a specific need for an improved indicator for displaying the open/closed state of the contacts of power circuit breakers, network protectors, and switches.
In particular, there is a need for an improved indicator which provides a fail safe display of the state of the contacts, especially should the contacts become welded closed.